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3.7.1 Virtual SCSI
Virtual SCSI refers to a virtualized implementation of the SCSI protocol. Virtual SCSI is based
on a client/server relationship. The Virtual I/O Server logical partition owns physical disk and
resources and then acts as server or, in SCSI terms, target device to share these devices with
client logical partitions.
Virtual I/O adapters (virtual SCSI server adapter and a virtual SCSI client adapter) are
configured using an HMC. The virtual SCSI server (target) adapter on the Virtual I/O Server is
responsible for executing any SCSI commands it receives. The virtual SCSI client adapter
allows a client partition to access physical SCSI and SAN attached devices and LUNs that
are assigned to the client partition. The provisioning of virtual disk resources is provided by
the Virtual I/O Server.
Physical disks presented to the Virtual l/O Server can be exported and assigned to a client
partition in a number of different ways:
The entire disk is presented to the client partition.
The disk is divided into several logical volumes, which can be presented to a single client
or multiple different clients.
As of Virtual I/O Server 1.5, files can be created on these disks and file backed storage
devices can be created.
The Logical volumes or files associate with a single SCS or Fibre Channel adapter can be
assigned to different client partitions. Therefore, virtual SCSI enables sharing of adapters and
also disk devices.
Figure 3-4 shows an example where one physical disk is divided into two logical volumes by
the Virtual I/O Server. Each of the two client partitions is assigned one logical volume, which
is then accessed through a virtual I/O adapter (VSCSI Client Adapter). Inside the partition,
the disk is seen as a normal hdisk.
Figure 3-4 Architectural view of virtual SCSI
Chapter 3. Virtualization
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